1. Field of the Invention
The invention relates to radar reflectors for enhancing the radar cross section or visibility of objects to which they are attached.
2. Discussion of Prior Art
GB2194391 discloses a passive radar target formed of a solid spherical dielectric lens with a reflecting coating covering part of the spherical surface. By using material of the correct dielectric constant, radar waves incident on the uncoated surface of the lens from a wide range of directions are reflected back towards the transmitter. Such lenses can provide a substantially uniform radar cross section over a wide range of angles. Thus, an object can be constantly visible on a search radar in spite of movement of the object, as would be the case for example for a small boat.
GB Patent Application No. 9117662 discloses an alternative dielectric lens reflector arrangement using compound lenses. Two thin converging lenses of similar dielectric constant are used to refract incident radar energy to a metal coating applied to the outer face of one of the lenses. Such two lens arrangements have the advantage of reduced weight for the same radar cross section when compared with solid lenses.
The reflective portions of lens-reflector combinations have blind spots which can be overcome, depending on the application, by choosing particular orientations for the radar reflector.
For marine radar reflectors, the International Standard ISO 8729:1987(E) requires that the maximum echoing area of a radar reflector should be at least 10 m.sup.2 for all frequencies between 9.32 and 9.5 GHz. Uniformity of reflection is also required in that the azimuthal polar response diagram should have a response over 240.degree. of not less than -6 dB with respect to the maximum and the response level should not be less than -6 dB over any angle of more than 10.degree..